Process for preparation of a bleaching agent



United States Patent- Ofifice 3,227,655 Patented Jan. 4, 1966 3,227 ,655PROCESS FOR PREPARATION .OF A BLEACHENG AGENT Konrad Prett and KarlThurnher, Dornbirn, Austria, -assigners to FMC Corporation, New York,'N.'Y., a corporation of Delaware No Drawing. Filed Jan. 30, 1962, Ser.No. 169,950 1 Claim. '(Ci. 252.186)

This application is a continuation-in-part of U.S. patent applicationSerial Number 775,683, filed November '24, 1958, in the names of thepresent inventors, now abandoned.

This invention relates to a process of preparing bleach solutions whichcontain organic peracids. in high concen- 113131011, which solutions arehighly stable and therefore are particularly suited to being stored foruse at a desired time. These bleach solutions are suitable for bleaching.textile fibers in the 'form of loose fiber material as well as of spun,woven and knitted products consisting of native and artificial fibers ofcellulose or of synthetic fibers, and of pulp or pulp products.

The bleaching processes known at the present time have the disadvantagethat they deteriorate the various fiber materials in a higher or lowerdegree, or as in the .chlorite bleach, develop highly toxic fumes, anddestroy the materials of construction employed, particularly stainlesssteels. Most of these bleaching processes require a highly alkalinepretreatment or are carried out themselves in alkaline solutions whichcause an undesired change in the textile properties of the fibermaterials and promote a deterioration of these fiber materials bymolecular and atomic oxygen. Another disadvantage of most of theprevious bleaching processes resides in that a large number of even fastdyestuffs of the vat and naphthol types are varied in hue .or in .theirfastness properties by the bleach and only a relatively small number ofthese dyestuffs were suitable for .dyeing articles to be bleachedarticles so that the field of application of the bleaching of dyedarticles was highly restricted and increased in cost.

It is known that organic peracids, such as monoperacetic acid, have ableaching activity even in acid solutions and the bleach carried outwith these solutions does not have the above-mentioned disadvantages andthat monoperacetic acid is highly suitable for bleaching fabrics whichcontain vator naphthol-dyed eiiects. The direct ,use .of =monoperaceticacid for bleaching, however, involves very great difiiculties becausethe same cannot be used on a large scale owing to its relatively highcost and the danger of explosion inherent in highly concentratedsolutions thereof.

For bleaching with peracids it has been necessary therefore, to formthem in the bleach solutions by the action of hydrogen peroxide or otherperoxides on the corresponding acids or .acid anhydrides. A number ofprocesses are known in which peracids are formed in concentrated ordilute solutions. These processes have not been successful because ofthe small yields and the danger involved. For instance, peracetic .acidcan be obtained by the actionof concentrated solutions of hydrogenperoxide on acetic .anhydride .in the .presence of sulfuric acid or acidsalts. This leads to sudden, high temperature rise and spontaneousdecomposition. For this reason this process is not suitable forbleaching plants. It is also known that peracids or their salts can beobtained by the action of the peroxide solution on alkaline solutions ofanhydrides of organic acids. This reaction is successful only at arelatively high pH, preferably between 8 and 11, and in dilutesolutions. For higher concentrations at these pHs, that is above about12 volumes or 3.5% of active oxygen expressed as hydrogen peroxide,solutions such as are used for replenishing used bleach solutions, orfor continuous bleaching in vessels with .a prosaturated with bleachsolution, and in contacting the wetted fibers with bleach, theconcentration of the bleach solution is reduced. Thus, starting with ableach solution containing peracetic acid in the amount of about 2 to3.5%, that is an amount of active oxygen corresponding to that in 4 to7% of hydrogen peroxide, the bleach bath is diluted to a point where it.contains only about 0.5% of peracetic acid, which corresponds to about1% of hydrogen peroxide on an active oxygen basis. This .is the amountwhich typically, actually is required for bleaching. Use of a peraceticacid bleachsolution having an excessive pH involves also deteriorationof the fiber during bleaching, and is necessary in this process .toreduce the pH by an addition of acids to the value required forbleaching with peracids. This involvesan additional consumption ofacids, in cases where the H .is on the order of 8 to 11.

It is a feature of this invention to provide aqueous peracetic acidsolutions for the bleaching of fibers in which the solutions have a highactive oxygen content, .yet are stable against decomposition of theactive oxygen even when the solutions are prepared foruse as much as aday or more before they are used.

It has now been found, quite surprisingly, that such stable peraceticacid solutions, vhaving an active oxygen concentration of at least 12volumes (3.5% expressed as hydrogen peroxide, or 1.75% expressed as.peracetic acid), can be prepared from hydrogen peroxide and acetic.anhydride by reacting these reagents in an aqueous medium at a pH ofabout 2 to no greater than about 4, in the presence of ammonium ionsintroduced .in the form of ammonia, ammonium hydroxide, or organic,primary, secondary or tertiary amine bases such as pyridine,monoethanolamine, triethanolamine, and the like. 'The ,action of theseadditives does not only depend on their basic character, which enablesthem to substitute alkali, but also on their pronounced catalyticactivity, whereby the ion equilibrium of the mixed solution is displacedtoward the peracetic acid which is being formed. This displace- .ment ofthe ion equilibrium takes place readily not only at pH-values above 8,as with other alkalies, but is also achieved with pH values in the lowranges of 2 to 4. Furthermore, the peraceticacid formed is stable at aPH in this range. It has been observed that the pH of the solution isadjusted within a few seconds to a final value,

whereas the formation of peracetic acid does not begin immediatelybecause a considerable amount of organic peroxide is formed first, whichsplits to form peracetic acid only after the reaction has proceeded forsome time. The bleach solutions .thus obtained exhibit :a particularlygood bleaching activity particularly on native cellulose fibers. It isbelieved that the presence .of ammonium bases has a favorable effect onthe bleaching process and assists particularly in the removal of thenatural waxes.

The ratio between the peractic acid formed and "the nonreacted hydrogenperoxide still in solution .can be determined by titration withpotassium permanganate and subsequent addition of potassium thiosulfate.Favorable bleaching results will be obtained if at least 65% of thehydrogen peroxide used is reacted to form peracetic acid. The bleachingactivity of the solutions is appreciably reduced if the peracetic acidcontent is below this value. According to the process of the invention,it is possible, however, to obtain almost complete reaction of thehydrogen peroxide to form peracetic acid when the said additives arepresent. It has been found that native and artificial cellulose fiberscan be bleached with these solutions Without chemical deterioration ofthe cellulose if the content of non-reacted hydrogen peroxide does notexceed 35% of the hydrogen peroxide charged. The determination of thedegree of fluidity has shown that the same is not appreciably higherthan before the treatment.

The solutions have given satisfactory results in the bleaching ofmaterials dyed with almost all known vat or naphthol dyestuffs withoutcausing changes in the hue of fastness of these dyestuffs. The bleachsolutions prepared according to the invention may be used in practicallyall conventional bleaching apparatus. Acid-resisting materials such asceramics, synthetic resins and particularly stainless steels may be usedas maerials of construction particularly of those parts of suchapparatus which are contacted by the bleach solution. Such materials arenot attacked by these bleach solutions. It has been found that theoptimum bleaching temperature is in the range of 6090 C., althoughtemperatures as low as about 25 C. can be used if the solution has ahigh active oxygen concentration, e.g., at least about 4 to 5% expressedas hydrogen peroxide. The vessels in which the bleach is performed aresuitably closed against the environment or covered because peraceticacid is somewhat volatile at these temperatures.

The optimum pH-value for bleaching depends on the material to bebleached. A preferred range is between 4.5 and 6, and the presentsolutions can be brought to this level by addition of phosphate,particularly tetrasodium pyrophosphate, or other alkali to the bleachingsolution. Addition of phosphates also avoids undesirable catalyticeffects and a contamination of the material to be bleached, or of theprocess water, with iron, manganese and copper.

The bleaching operation will normally be conducted with the presentperacetic acid solutions containing active oxygen in an amountcorresponding to that in about 1% of hydrogen peroxide; this amounts toabout 0.5% of peracetic acid. The amount of active oxygen, can however,be as much as 4 to 5% expressed as hydrogen per-oxide, or 2 to 2.5%expressed as peracetic acid, if bleaching temperatures are not permittedto exceed about 25 to 35 C. Intermediate concentrations of active oxygenwll be employed with temperatures intermediate the 25 C. to 35 C. rangeand the 60 to 90 C. range.

The bleach solutions may be directly prepared in the concentrationsrequired for bleaching, in accordance with the following examples, or ina concentrated form for replenishing used bleach liquors or as stocksolution for a quick preparation of bleach liquors. The concentratedstock solutions may contain active oxygen in a concentration of up toabout as hydrogen peroxide, or 5% as peracetic acid. More highlyconcentrated solutions tend toward instability. It is suitable topreclean the material to be bleached and to remove any size from wovenfabric by a desizing treatment. A pretreatment with strong causticalkali baths, as is usual for bleaching native cellulosic fibers, can beemployed but is not essential unless bleaching to pure white is desired.It is also possible to apply a weak treatment with other bleachingagents, such as sodium hypochlorite, before or after bleaching with thepresent bleach solution. This weak treatment may be carried out in aconcentration which is so low that it does not cause a deterioration ofthe fiber material.

The following examples illustrate the invention, but the latter is notlimited thereto.

Example 1 A peracetic acid solution suitable for use directly as ableach solution, or dilutable to form a mote dilute bleach 4 solution,was prepared by mixing the following ingredients. The temperature of thereaction mixture rose to about 171 F. during the reaction.

Water 224 Ammonium hydroxide (30% as NH 41 Hydrogen peroxide, 35% byweight 348 Acetic anhydride 387 The solution reached a final pH of about3.1. The following percentages of the added hydrogen peroxide reacted:

Percent After 15 minutes 81.5 After 60 minutes 86.1 After minutes 86.5

Ninety-three percent of the peracetic acid formed was retained after 24hours, whereas a similar solution at pH 5,5, containing the amount ofammonium hydroxide required to provide that pH, retained only 5% or lessof the peracetic acid after storage for a 24-hour period. Storage inboth cases was at 24 C.

Example 2 The procedure of Example 1 was followed, with the temperatureof the solution on mixing of the following ingredients reaching 146 F.

Water 388 Ammonium hydroxide (30% as NH 35 Hydrogen peroxide, 35% byweight 260 Acetic anhydride 317 The solution reached a final pH of about3.3. The following percentages of the added hydrogen peroxide reacted:

Percent After 15 minutes 90.4 After 60 minutes 93.4 After 120 minutes92.9

The procedure of Example 1 was followed, with the temperature of thesolution on mixing of the following ingredients reaching 121 F.

Ml. Water 508 Ammonium hydroxide (30% as NH 30 Hydrogen peroxide, 35% byweight 206 Acetic anhydride 256 The solution reached a final pH of 3.6.The following percentages of the added hydrogen peroxide reacted:

Percent After 15 minutes 91.1 After 60 minutes 93.8 After 120 minutes92.9

Ninety percent of the peracetic acid formed was retained after storagefor 24 hours at 24 C., whereas a similar solution containing sufficientammonium hydroxide to create a pH of 5.5 retained only about 25% of theperacetic acid formed after similar storage.

Example 4 The rocedure of Example 1 was followed with the temperature ofthe solution on mixing of the following in gredients reaching 106 F.

M1. Water 637 Ammonium hydroxide (30% as NH 35 Hydrogen peroxide, 35% byweight 146 Acetic anhydride 182 The solution reached a final pH of 3.9.The following percentages of the added hydrogen peroxide reacted:

Percent After 15 minutes 90 After 60 minutes 94 After 120 minutes 94.1

After 24 hours storage at 24 C., 80% of the peracetic acid formed wasretained, whereas when a similar solution was prepared at pH 5.5 with anamount of ammonium hydroxide required to provide that pH, only about 40%of the peracetic acid formed was retained, after storage under similarconditions for similar times.

Example 5 Water liters 67 Ice k Monoethanolamine kg 0.75 Hydrogenperoxide, 35% by weight liters 10 Acetic anhydride do 12.5

Ice is added to the above reaction mixture to prevent a temperature riseabove 35 C. Alternatively, the mixture may be cooled by means of coolingpipe coils.

The following percentages of the added hydrogen peroxide reacted:

Percent After 30 minutes 45 After 60 minutes 63 After 90 minutes 68After 120 minutes 71 After 300 minutes 73 The solution is ready for useafter a reaction time of about 3 hours.

Example 6 Water liters 67 Ice kg 10 Triethanolamine kg 0.9 Hydrogenperoxide, 35% by weight liters 10 Acetic anhydride do 12.5

The pH value of the finished solution is 2.7. The following percentagesof the added hydrogen per- A special cooling of this reaction mixture isnot necessary where Water at less than 12 C. is available. The pH-valueof the finished solution is 2.7.

The following percentages of the added hydrogen peroxide reacted:

Perc'ent After 30 minutes 63 After 60 minutes After minutes 72 Afterminutes 72 After 300 minutes 77 The bleaching agent solutions describedin Examples 5, 6, and 7 are concentrated stock solutions, which aredurable for two or three days and may be used for bleaching in thefollowing manner:

One hundred kilograms of knitware of polyamide fiber material are placedinto a circulating device of stainless steel and treated with a solutionto which 10 liters of a stock solution according to Example 5 or Example6 or 5 liters of a stock solution according to Example 7 have beenadded. Because these solutions have a low pH-value, sodium pyrophosphateor, if desired, some caustic soda is added to the solution to raise thepH-value of the solution to 4.5-5. The bleach solution thus prepared iscaused to circulate at a temperature of 60 -90" C., through the materialto be bleached. The bleaching is effected within one to two hours at atemperature of 60-90 C. This is followed by warm and cold rinsing anddrying. Other fiber materials such as linen, regenerated cellulose,rayon, pulp and pulp products etc., may be bleached with similarsuccess.

We claim:

A process of preparing a stable, concentrated aqueous solution of ableaching agent containing monoperacetic acid for bleaching fibermaterials, which comprises reacting hydrogen peroxide and aceticanhydride in an aqueous medium in the presence of ammonium hydroxide,said hydrogen peroxide being employed in an amount which provides anactive oxygen content of at least 12 volumes in said bleaching agentsolution, and said ammonium hydroxide and acetic anhydride being presentin amounts which provide a pH of 2 to 4 in said bleaching agentsolution, and carrying out the reaction until no more than 35% of thehydrogen peroxide introduced is present as hydrogen peroxide, and atleast 65% of the introduced hydrogen peroxide has reacted with saidacetic anhydride to form monoperacetic acid.

Conant et al.: The Chemistry of Organic Componds, 1959, 5th ed.,MacMillan Co., New York, page 162.

Alkanolamines and Morpholines, pub. by Union Carbide Chemical Co., NewYork, 1958, pages 4 and 5.

JULIUS GREENWALD, Primary Examiner.

ALBERT T. MEYERS, Examiner.

